Re: [XENBUS PATCH v3 1/2] Use Windows 10 APIs to inflate/deflate balloon

[Paul Durrant <xadimgnik@xxxxxxxxx>]

On 13/06/2025 11:41, Tu Dinh wrote:
> On 13/06/2025 12:36, Paul Durrant wrote:
> > On 12/06/2025 12:00, Tu Dinh wrote:
> > > Currently the balloon driver allocates pages as normal memory, which
> > > causes Windows to report the ballooned memory as kernel-allocated
> > > instead of unavailable.
> > >
> > > Windows 10 provides MM_ALLOCATE_AND_HOT_REMOVE to remove pages from
> > > the physical memory pool. The removed pages can be added back with
> > > MmAddPhysicalMemory.
> > >
> > > Using this feature, the real VM memory capacity will be correctly
> > > reported in Task Manager.
> > >
> > > Balloon deflation is implemented using calls to MmAddPhysicalMemory on
> > > contiguous PFN ranges.
> > >
> > > Note that MM_ALLOCATE_AND_HOT_REMOVE actually removes the pages from
> > > memory space, so the resulting MDL will have the MDL_IO_SPACE flag;
> > > similarly, when probing the freed MDL on deflation, we'll also have to
> > > set MDL_IO_SPACE.
> > >
> > > Signed-off-by: Tu Dinh <ngoc-tu.dinh@xxxxxxxxxx>
> > > ---
> > > v3: Fix the issue where hot-removed memory will be in I/O space.
> > > v2: Updated commit message to say what the patch does. No code change.
> > > ---
> > >    src/xenbus/balloon.c | 43 ++++++++++++++++++++++++++++++++++++++-----
> > >    1 file changed, 38 insertions(+), 5 deletions(-)
> > How much testing has this had? v3 came out of nowhere.
> The v3 fix came from manually testing the ballooning feature with a
> debug build under Driver Verifier (standard + a few extra checks). Aside
> from that I've done CodeQL and VS code analysis on the driver.
>
> On a side note, the Xen PV drivers use old annotations which are not
> checked by VS. Is there interest in upgrading to SAL 2.0? I tried doing
> so with xenbus and it caught a couple small issues.
Series applied